HEI Help ?

[54blackhornet]

I took the last few days and switched over from points to a GM HEI unit. I got it from a guy years ago. Been sitting in my shop. After installing it last night I turned the key and nothing. Question ? Rebuild it or get another complete unit. I have read that the module is prone to failure, replace it first ? I did run a dedicated 12 V wire from the fuse box...thanks again

[Steeveedee]

Are you dead certain that the power wire truly has power when cranking? Did you plug it into the "IGN Unfused" spot? If not, it may not have power during cranking, just in the "run" position. The first thing I would check is the rotor to make sure that it isn't burned through. That's the most common failure, in my experience. If you have high secondary resistance the 'trons will burn through the rotor to ground on the distributor shaft. If you have a high-impedance ohm meter you can trouble shoot the ignition. There's a thread by a guy named "Sharky"(?) around here somewhere that covers troubleshooting quite well.

[RustyPile]

Originally Posted by 54blackhornet

I took the last few days and switched over from points to a GM HEI unit. I got it from a guy years ago. Been sitting in my shop. After installing it last night I turned the key and nothing. Question ? Rebuild it or get another complete unit. I have read that the module is prone to failure, replace it first ? I did run a dedicated 12 V wire from the fuse box...thanks again

"Nothing"?? As in starter not engaging and turning the engine over?? Or engine cranking over but not running?? Can you be more specific please....

[Willys_MB]

I think "nothing" probably means you have a different issue. If you pull the HEI, you can check all the specs on it, they're available online. I checked my ancient HM HEI and found the end paly was out of spec by more than 4 times. I replaced the whole HEI with a Chairman Mao special on Amazon for ~$60 and got it running to buy me time to rebuild the GM unit with quality parts. I probably won't rebuild it until this Chinese one dies. 1-2k miles on it and no issue yet.

[54blackhornet]

Engine spins over fine just no ignition. I will double check that I have power at the BAT connection on the HEI itself today and check back in...

[68 P.O.S.]

Since it's a GM unit, I would rebuild it. Modules usually get the blame, but a lot of times the coil may be going bad and they can take out modules very quickly. I doubt this is your problem, but did you make sure to replace the original power wire? It has a resistor in it and is not meant for use with HEI. It will still run with it in place, but not very well haha.

If you rebuild it, give it a nice tune-up. Rotor, cap, coil, module, power wire, adjustable vac advance w/ springs, #41 advance weights and #375 center plate.

This site has some troubleshooting as well https://www.gmcmi.com/wp-content/upl...stributors.pdf

['68OrangeSunshine]

And don't forget to check the pick up coil, under the distributor weight plate. Those go bad and it's No Go.

[kwmech]

You got the rotor in the same position as the one you took out??

[MARKDTN]

So you checked for spark and there is none? I agree with the above-12v to the coil with a new wire replacing the resistor wire, make sure the pickup is plugged in, good coil, etc. 30 years ago the Delco or NAPA modules were the only ones to have. Not sure if that is true anymore, but probably as good as any. The end play is pretty easy to fix with shims. I don't know, I'll old fashioned, I would rebuild what you have way before buying a new offshore unit. GM HEIs are not that hard to find and there were a lot made. You will want to be sure your advance is working properly when you get it started, they do have a tendency to stick over time.

[54blackhornet]

Well I figured out why I had no spark from the HEI , I installed a 10 amp blade fuse inline. I looked closely at the fuse and noticed it was blown. New fuse and I have fire ! Problem is I have the timing off because it keeps backfiring while turning the key. I have reread the procedure on getting the #1 piston up to TDC but still having a problem actually accomplishing it. I doing this by myself so it’s harder then having a assistant. I have a remote starter but can’t seem to get the alligator clip onto the small starter post to use it. I gave up with frustration. Should I find a piston stop ? Or a helper.

[demian5]

Basically line up the timing mark on the balancer with the pointer at 0. Its either right on or 180 degrees off.

Then install the distributor with the rotor pointing toward the number 1 cylinder (left front of engine). Use a long screwdriver to rotate the oil pump shaft to line it up (this is always trial and error for anyone).

Put the cap on and have the connectors oriented to where they are 90 degrees from the engine on the driver side, then put #1 plug wire in the terminal in front of the connector box thing, then 18436572 with 2 being on the opposite side of the connector box thing on the cap.

With the distributor loose enough to turn but tight enough to hold firm in place, turn the distributor to where you feel the #1 terminal matches the rotor location and try and start it.

If it wants to start, rotate the distributor either way until it starts. If it wont start or pops really bad no matter what, the distrinutor is 180 degrees out, so line up the mark again on the balancer with the timing mark and look where the distributor is. Pull it and get the rotor pointing the opposite way. Plug wires should still be good as you are going to put it all back together the same way (don't forget to rotate the distributor body all 180 degrees so the cap fits right).

Hope this makes sense..

[geezer#99]

I used my compression gauge to find tdc #1.
Hung it up to the hood with a string so I could see it while bumping it over.

[Wrenchbender Ret]

Don't ever put a fuse in the circuit to the dist. Especially a 10 amp. If you feel you must have a fuse in that circuit use a 40 amp. These HEI dists can have a surge. Thats why they use a 10-12 gauge wire to supply them. If that little fuse blows when you are going down the freeway bumper to pumper you could be in big trouble.
George

[RichardJ]

Actually GM used a 14 gauge wire for the HEI distributor. Unlike most chassis wiring that remains stationary for years on end, they realized the dist needed to be periodically rotated to adjust timing. The insulation on the 14 ga dist wire is larger and softer than normal 14 ga wire.

The image below is from '75 Chevy truck shop manual.

The stock GM HEI draws 2 Amps. I've measured them at closer to 1.5 Amps

If you see any voltage spike at the HEI distributor, it's because you didn't remove the wire from the "I" terminal on the starter solenoid. If the little tang on the inside of the solenoid "I" terminal is bent out of place, the EMF from the collapsing magnetic field in the solenoid coils could fry the HEI module.

[54blackhornet]

Richard could you elaborate on the original wire from the starter solenoid ? I don’t understand completely what you are saying ? I have a 12G wire running directly from the fuse box. So I should remove the inline fuse to the HEI ? The compression gage idea is a great thought thanks..Jack

[Accelo]

RichardJ:
How can the clock be 5-amps?
Must be a mistake and it should be .5A?

Thanks good information.

[RichardJ]

The "I" terminal on the solenoid was used to provide a by-pass circuit for the points type ignition coil.

The starter motor draws 250-300 Amps or MORE when cranking the engine. That can pull the 12.5Volt battery down to 10 Volts or less while cranking. The points ignition circuit (copper wire, various connectors, ign switch, neutral switch, ballast resister) can drop the voltage another 2-3Volts to the ign coil.

The HEI isn't as particular. it can produce secondary ignition voltage from as little as 8 volts.

The starter solenoid can draw 45 Amps to engage the starter. Once engaged, the solenoid Hold-In winding draws 12Amps. That 12 Amp winding generates a large magnetic field. When the Ign key is released and the magnetic field collapses, a EMF as high as 400 volts is generated.
If the tang under the "I" terminal and that big washer flopping around in there contact each other, the HEI module is toast.
A voltage spike like that to the points ignition would mean nothing. Remember, every time the Ign points open, the collapsing magnetic field in the ignition coil generates 200-300 volts across the Ign points. What's one more voltage spike.

Not only is the "I" terminal connection not needed, it also can be detrimental.

[RichardJ]

A 5 Amp clock.

If you know how those old clocks work, I guess it could be that high. The instant the contacts touch it winds itself for 3-4 minutes.
The contacts are going to be closed for maybe a millisecond, so the actual current draw from the battery is minimal.

[54blackhornet]

Richard you have a much higher knowledge level then most, I appreciate your input. So how do you eliminate that from happening ? Completely remove the yellow wire along with the post it connects to ?

[RichardJ]

>> Completely remove the yellow wire along with the post it connects to ? <<

The wire from the "I" terminal (yellow or what ever), is spliced into the resistor wire and the copper wire that goes to the coil. On a six cyl, that splice is located inside the harness alongside the valve cover above the #4 plug. On a V8 the splice is behind the passenger head, next to the bellhousing.

Remove the wire from the "I" terminal, bend it back over itself and tape it up is the simple way. What you do with the other end is up to you, depending on if you actually removed the resistor wire from the truck.

For me, I'm still using the resistor wire and have been for 30 years.

Originally the resistor powered a six cyl HEI with coil in cap. When I installed the AC, i switched it to a External coil HEI.

With the Alt charging at 14Volts, the HEI gets 11.5 Volts. More than enough.

[Happy_dan]

There are lots of threads about getting TDC set. Here is what I did. I removed all the plugs so no heavy compression. Put a socket on the balancer bolt and my thumb over number one spark plug hole until I felt compression. Then moved the timing mark to 0. Set the rotor to point at plug number one. I was still off one tooth, but was able to figure that out pretty easy since I was able to see timing mark and it was far off. I was able to do this with no help. Then I put all plugs back in and started it up and set timing with light.

[54blackhornet]

First I would like to thank everyone for all the help. Yesterday afternoon late I finally managed to get TDC set properly. Only took about a half dozen tries. The little 307 started up on the first turn. With the recent carb overhaul she runs better than it ever has. Doing this by myself was a major accomplishment and could not have done it without you guys assistance...thanks..Jack

[Happy_dan]

Love it!! Congratulations and couldn't agree more on how helpful this board and it's members are. They sure teach me a lot.

[Cap'n Hook]